Analysis of mode-locked internally frequency doubled broad-band continuous wave lasers

Closed-form analysis of pulse evolution in the transient regime in an actively modelocked internally frequency doubled broad-band continuous wave laser is presented. The analysis enables investigation of the effect of nonlinear crystal inside the laser cavity on mode-locked pulse parameters at the fundamental frequency. It is shown that the presence of internal second harmonic crystal broadens the fundamental mode-locked pulse while accelerating the approach of the system to steady-state. The dependence of pulse parameters on the bandwidth of the tuning element, modulation depth of the active mode-locker and conversion efficiency of the frequency doubler is presented in detailed graphical form.     

In-tandem deposition and sintering of printed gold nanoparticle inks induced by continuous Gaussian laser irradiation

By employing continuous Gaussian laser irradiation in tandem with a specifically designed drop-on-demand jetting system, nanoparticle inks were printed and sintered on glass substrate. A toluene solvent is employed as the carrier of gold nanoparticles possessing a lower melting temperature than that of bulk gold. Marangoni flow due to radial surface tension gradient combined with a moving substrate displaces nanoparticle ink in front of and around the laser spot. Experiments were carried out changing incident laser power, focused beam waist, and translation speed, and resulting phenomena at different conditions were explained. Strong coalescence occurred from 9000–14000 W/cm², and a gold line with 8 m of width was demonstrated. PACS 81.16.Mk; 85.40.Ls; 44.10.+i; 47.20.Dr     

Superresolution imaging of DNA tetrahedral nanostructures in cells by STED method with continuous wave lasers

DNA tetrahedral nanostructures are considered to be uew nanocarriers because they can be precisely controlled and hold excellent penetration ability to the cellular membrane. Although the DNA tetrahedral nanostructure is extensively studied in biology and medicine, its behavior in the cells with nanoscale resolution is not understood clearly. In this letter, we demonstrate superrcsolution fluorescence imaging of the distribution of DNA tetrahedral nanostructures in the cell with a simulated emission depletion （STED） microscope, which is built based on a conventional eonfocal microscope and can t）rovide a resolution of 70 nm.     

Statistical temporal behaviour of pulse wave propagation through continuous random media

Pulse waves propagating through random media suffer distortions, such as fluctuation of arrival time, temporal broadening, and alteration of skewness and kurtosis, due to both the background medium and embedded irregularities. We carry out a study on the temporal behaviour of electromagnetic pulses propagating through random media using temporal moments and an analytic solution of a two-frequency mutual coherence function recently obtained by iteration. We treat the temporal characteristics sequentially, with general expressions obtained first. Then the concise forms are given for pulse propagation in the turbulent non-dispersive atmosphere and the ionosphere, with numerical calculations for the latter. The results show that the mean arrival time is dominated by the term propagating at group velocity, and small corrections arise from higher-order dispersion of the background medium and random scattering of irregularities, but the correction from dispersion of irregularities is neglected as it is so small. As for pulse broadening in trans-ionospheric propagation, the results show that contributions are mainly from the dispersion of the background ionosphere and scattering of electron density irregularities in most cases, and the contribution of dispersion of irregularities is so small that it can be neglected. Finally, we find that the temporal skewness of a trans-ionospheric pulse is negative and its energy is shifted to the leading edge, and the contributions from scattering and dispersion of irregularities dominate over those of background, so the latter can be neglected in most cases.     

Modelling of excited state absorption and upconversion in erbium germanosilicate continuous wave fibre lasers

The effects of upconversion and pump excited state absorption (ESA) on a three-manifold continuous wave (CW) laser are investigated by solving the laser and pump differential equations subject to two-point boundary conditions. This technique is applied to erbium germanosilicate fibre lasers in low-finesse cavities. First, the three-manifold laser problem in a low-finesse cavity is solved analytically, without ESA and upconversion. This shows that the finite value of the upper pump manifold decay rate causes the extracted power to saturate, and it also shows that pump threshold is strongly influenced by the cavity reflectivity. Next, upconversion and ESA are included. This leads to a study of the extracted power and pump threshold as functions of fibre length and outcoupling. This simulation is numerical and is successfully anchored to experiment.     

Low temperature sintering of sub-stoichiometric Ni-Cu-Zn ferrites: Shrinkage, microstructure and permeability

We have studied sub-stoichiometric Ni-Cu-Zn ferrites with iron deficiency (i.e., <50mol% Fe₂O₃) of composition Ni_0.20Cu_0.20Zn_0.60+zFe_2−zO_4−(z/2) with 0≤z≤0.06. The temperature of maximum shrinkage rate is shifted from T=1000 °C for z=0 towards lower temperatures down to T=900 °C for a sub-stoichiometric ferrite with z=0.02. Dense samples are obtained after firing at 900 °C for z>0 only. Sub-stoichiometric compositions (z>0) do not form single-phase spinel ferrites after sintering at 900 °C, but rather represent mixtures of CuO and a stoichiometric ferrite with slightly modified composition. The formation of small amounts of CuO at grain boundaries is demonstrated by XRD and SEM. The permeability is increased from μ=80 for stoichiometric ferrites (z=0) to μ=660 for z=0.02. The formation of CuO during sintering of sub-stoichiometric ferrites supports densification and is a prerequisite for low temperature firing of multilayer inductors. Addition of 1 wt% Bi₂O₃ as liquid phase sintering aid is required to provide sufficient densification of the stoichiometric ferrite (z=0) at 900 °C. Addition of 0.37 wt% Bi₂O₃ to a sub-stoichiometric ferrite (z=0.02) results in dense samples after firing at 900 °C; however, the microstructure formation is dominated by heterogeneous grain growth.     

The use of diode array detectors in conjunction with continuous wave gas lasers for anti-Stokes Raman spectroscopy

The Raman spectrum of any molecule consists of two mirror-image signals, th e Stokes and anti-Stokes Raman spectra. In most cases, unless highly specific sampling conditions are used, the anti-Stokes signal is much weaker than that of the Stokes. The recent application of intensified diode array detectors to Raman spectroscopy has produced a marked increase in the sensitivity of the technique which makes a study of the anti-Stokes spectrum potentially more rewarding than it has been to date. The present study has shown that, although of limited use for general purposes, there are some specific instances where the anti-Stokes spectrum can be of considerable practical use. Such applications are to extend the operating range of the Raman spectrometer, to study photodegradable samples and for the analysis of samples which exhibit strong fluorescence.     

Room temperature continuous wave visible vertical cavity surface emitting laser

Visible VCSEL laser operated at room temperature continuous wave has been achieved by H+ implants using tungsten wires as an implantation mask. The laser wavelength is 650 nm, and the maximum output without heat-sink exceeds 85 W at CW operation. We also calculated the thermal resistance of the device.     

Control of spectral lines weakly absorbed by atmosphere in continuous wave chemical HF lasers

The behavior of two lines P _1-0(11) and P _2-1(8) weakly absorbed by the atmosphere is experimentally investigated in the spectra of cw chemical multikilowatt HF lasers of five types that differ in size and construction scheme of the nozzle array. It is shown that the intensity of these lines can be controlled within certain limits by varying the gas-dynamic regime of the laser operation, the chemical composition of the active medium, the orientation of the optical axis of the cavity and the cavity feedback factor, and the construction of the nozzle array.     

Low temperature microwave sintering of yttrium and samarium co-doped ceria solid electrolytes for IT-SOFCs

Nanocrystalline co-doped ceria Ce_0.8Sm_0.2?xY_xO_2?δ solid electrolytes for intermediate-temperature solid oxide fuel cells (IT-SOFCs) were synthesized through sol–gel auto-combustion method. The prepared samples were sintered via microwave sintering at 1200 °C for 1 h. The X-ray diffraction analysis of co-doped ceria system reveals formation of the samples with a single-phase cubic fluorite structure. The lattice parameter values were calculated from X-ray diffraction patterns. The calculated crystallite sizes of all the samples were found to be in the range of 17 and 28 nm. Surface morphologies and elemental analysis of all the samples were carried out by using SEM and EDS analysis. The existence of chemical bonding in the samples was studied by FTIR spectroscopy. The presence of oxygen vacancies and evaluation of their concentration in the material was carried out using Raman spectroscopy analysis. Electrical properties of all the samples were analyzed by impedance spectroscopy. It was found that microwave sintered co-doped ceria sample Ce_0.8Sm_0.1Y_0.1O_2?δ exhibits the highest total ionic conductivity with minimum activation energy among all the compositions and conventional sintered sample. Therefore, it can be concluded that the microwave sintered Ce_0.8Sm_0.1Y_0.1O_2?δ sample may be useful as a promising electrolyte material for the IT-SOFCs.     

端面抽运Tm，Ho∶YLF连续激光器的参数优化与实验研究

研究了激光二极管端面抽运Tm,Ho∶YLF连续激光器的输出特性,并对激光器的参数进行了优化.在考虑能量传递上转换的前提下,通过准三能级速率方程推导出了连续抽运Tm,Ho∶YLF激光器输出功率与抽运功率关系的表达式.对激光晶体的粒子掺杂浓度、晶体长度、激光束腰半径与抽运光束腰半径比值以及输出镜透过率等激光器参数进行了优化.实验上得到了激光输出功率随抽运功率的变化关系,并将其与理论结果进行了比较,发现比较吻合,从而验证了理论模型的合理性. 关键词： Tm Ho∶YLF晶体 速率方程 能量传递上转换 参数优化     

Femtosecond fiber lasers with pulse energies above 10 nJ

A series of experiments aimed at determining the maximum pulse energy that can be produced by a femtosecond fiber laser is reported. Exploiting modes of pulse propagation that avoid wave breaking in a Yb fiber laser allows pulse energies up to 14 nJ to be achieved. The pulses can be dechirped to sub-100-fs duration to produce peak powers that reach 100 kW. The limitations to the maximum pulse energy are discussed.     

Ultra-low temperature sintering of Cu@Ag core-shell nanoparticle paste by ultrasonic in air for high-temperature power device packaging

Sintering of low-cost Cu nanoparticles (NPs) for interconnection of chips to substrate at low temperature and in atmosphere conditions is difficult because they are prone to oxidation, but dramatically required in semiconductor industry. In the present work, we successfully synthesized Cu@Ag NPs paste, and they were successfully applied for joining Cu/Cu@Ag NPs paste/Cu firstly in air by the ultrasonic-assisted sintering (UAS) at a temperature of as low as 160 °C. Their sintered microstructures featuring with dense and crystallized cells are completely different from the traditional thermo-compression sintering (TCS). The optimized shear strength of the joints reached to 54.27 MPa, exhibiting one order of magnitude higher than TCS at the same temperature (180 °C) under the UAS. This ultra-low sintering temperature and high performance of the sintered joints were ascribed to ultrasonic effects. The ultrasonic vibrations have distinct effects on the metallurgical reactions of the joints, resulting in the contact and growth of Cu core and the stripping and connection of Ag shell, which contributes to the high shear strength. Thus, the UAS of Cu@Ag NPs paste has a great potential to be applied for high-temperature power device packaging.     

Electro-optically Q-switched lasers with polarization output coupling and their pulse control

We present a design of E/O Q-switched laser with polarization output coupling. Based on laser rate equations, we analyzed pulse control of this type of laser. A model of laser pulse generating is set up. The relationship between pulse energy and high voltage values is given in this model. The experiments have been carried out. The result fits the theoretical model well.     

Some characteristics of dye lasers with nitrogen laser pulse excitation

Results from experiments in which the ultraviolet pulses from a nitrogen laser are used to obtain laser action from organic dyes are described. The dyes include three in the xanthene group (rhodamine 6G, B, and sodium fluorescein) and two coumarins, 7-diethylamino-4-methylcoumarin and 7-N-dimethylamino-4, 6-dimethylcoumarin) in ethanol solvent. With these dyes, laser power is available over the entire visible range from 4200 to 6300 Å when used with a rotatabie diffraction grating. The range of tunability of one of the dyes was extended to 1000 Å by appropriate acidification. The spectral halfwidth of the light varied between 7 and 15 Å over the range of tunability. Maximum repetition rates of 100 pps were obtained. Maximum power efficiency of 25% was found for rhodamine 6G. Overall output pulse shapes were found to be in agreement with the theory of Sorokinet al. Output pulse widths varied from 1 to 7 nsec. Other dyes which we have found to lase by this method of excitation include acridone, chloro-aluminium pthalocyanine and 4-methylumbelliferone. However, these dyes will not be discussed further in the text.Partially supported by US Army Research Office, Durham, North Carolina.     

Modeling and simulation of titanium dioxide nanoparticle synthesis with finite-rate sintering in planar jets

Numerical simulations of titanium dioxide nanoparticle synthesis in planar, non-premixed diffusion flames are performed. Titania is produced by the oxidation of titanium tetrachloride using a methane–air flame. The flow field is obtained using the two-dimensional Navier–Stokes equations. The methane–air flame and oxidation of titanium tetrachloride are modeled via one-step reactions. Evolution of the particle field is obtained via a nodal method which accounts for nucleation, condensation, coagulation, and coalescence with finite-rate sintering. The modeling of finite-rate sintering is accomplished via the use of uniform primary-particle size distribution. Simulations are performed at two different jet-to-co-flow velocity ratios as well as with finite-rate and instantaneous sintering models. In doing so we elucidate the effect of fluid mixing and finite-rate sintering on the particle field. Results show that highly agglomerated particles are found on the periphery of the eddies, where the collisions leading to nanoparticle coagulation occur faster than nanoparticle coalescence.